Caltrans Districts Headquarters - Stormwater Quality Monitoring Program - Maintenance Station Wash Racks Discharge Study

Vehicle washing in containment zone entrains pollutants in the wash water catchment system
Wash water recycle processing unit (RPU)
RPU effluent water sampling for characterizing discharge relative to effluent limits
Prime Contractor: 
Period of Performance: 
December, 2006 to June, 2007
Project Description: 

The Caltrans Maintenance Department was proposing to remove the Recycle Process Units (RPUs) from some of its wash rack facilities. The wash rack facilities selected for this study employed RPUs to recycle wash water for reuse. The purpose of this study was to characterize un-recycled wastewater generated during the vehicle washing process at each study location in order to verify that it could be safely discharged into leach fields. In addition, samples were collected from the effluent of the RPUs at selected study locations in order to evaluate RPU performance.

ADH, as a subcontractor, supported Caltrans sampling efforts by providing personnel to sample water discharging from the oil/water separators while maintenance crews were actively washing vehicles. ADH was responsible for performing aspects of the sampling program at five maintenance stations located within Caltrans Districts 1, 4 and 5, including Bracut-Eureka, Garberville, Willow Creek, Gilroy and King City. Samples were collected from three locations: pretreatment effluent, source water, and RPU effluent. The sampling at each site occurred during three mobilizations as follows:

Mobilization 1: Sample three vehicles for:

  • Primary Constituents List of pre-effluent
  • Generate field blank and field duplicate samples

Mobilization 2: Sample three vehicles for:

  • Source water and RPU effluent
  • Two Primary Constituents List of pre-effluent
  • One Expanded Constituents List of pre-effluent

Mobilization 3: Sample four vehicles for:

  • Three Primary Constituents List of pre-effluent
  • One Expanded Constituents List of pre-effluent
ADH Responsibilities: 
  • Coordinated sampling activities with respective Caltrans maintenance facility staff
  • Reconfigured wash rack piping at certain maintenance station using site-specific diagrams to allow for monitoring of wash water without influence of the RPUs
  • Collected Primary Constituents and/or for Expanded Constituents List
  • Coordinated efforts with analytical labs and prepared samples for overnight or same day delivery
  • Generated extensive field and corresponding photographic documentation, including monitoring vehicle and equipment washing discharges, and general observations of weather conditions, site conditions and concerns